1. Field of the Invention
The present invention relates to a collet-and-shank assembly device for gripping and securing work tools and work pieces used in various types of machining operations. More particularly, the present invention relates to a collet-and-shank assembly device that can be tightened or loosened from one end, and that provides for an increase in the space available to work on the piece to be machined. A unique locking nut of the present invention provides the means for single-end manipulation of the entire assembly device.
2. Description of the Prior Art
In the field of lathes, screw machines, and other similar rotary machining equipment, various tool- or work piece-holding devices have been designed to grip the tool or piece securely. The collet is a common element of such gripping devices. Collets are generally compressible tubes or sleeves that engage the work piece or tool in such a way that it either does not move, or only moves in the same way that the collet does. In most instances, the collet acts in conjunction with a closing element that surrounds the collet and provides uniform pressure to the entire outer perimeter of the collet. This closing element is typically a sleeve-like body that may be similar in appearance to the collet. The collet is designed such that when this uniform pressure is applied to it, its radial dimensions are reduced, and the tool or work piece located within the collet is locked in place. The means by which the closing element--generally a sleeve or shank with an inner diameter that is larger than the collet's outer diameter--applies pressure to the collet can vary. Prior to the application of such pressure it is necessary to first form the collet so that it can be uniformly compressed when pressure is applied to it. Of course, in order to remain effective through more than one use, the collet must be designed so that it can "spring" back to its original shape when that pressure is removed. This is achieved in prior gripping devices by providing the collet with a split end, i.e., making it a split-type collet. A split-type collet has an end region formed of several sections, each separated by slots or openings that, in effect, reduce the overall hoop strength of that end of the collet. Furthermore, the collet is tapered at the end region, with the several sections having the collet's greater outer diameter. The closing element that is used to apply uniform pressure to the collet is also tapered; however, its smaller outer dimension is that region that corresponds to and comes in contact with the collet's end region. Using means to draw the collet into the tapered closing element, the larger collet end region with its several sections and spacings is squeezed into the closing element's end region such that the several collet sections close in nearer each other, thereby reducing the outer and inner diameters of the collet. By placing the work piece or tool within the collet and then drawing the collet into the closing element, that tool becomes locked in position as a result of the reduction in size of the inner diameter of the end region of the tapered collet. Once the tool or work piece is locked in position, the collet and accompanying closing element are placed in the machining equipment.
One problem with the prior tool-securing devices that include collets is that they are designed such that the various components must be joined together from both ends of the assembly. That is, at one end of the collet--generally the end that is not tapered--a first securing component joins the collet to the closing element. At the opposite end--the tapered end of the collet--a second securing component on the outside of the closing element acts to compress the collet at that tapered end such that it grips the work piece or tool located in the bore of the collet. This second securing component may be a threaded ring joined to the closing element, it may be a nut affixed to the exterior of the closing element, or it may be a compressing sleeve of the type described in U.S. Pat. No. 2,783,051, issued to Stromme in 1957.
Regardless of the type of securing component or components used, the prior devices require manipulation at both ends of the assembly in order to secure the tool for machining operations. This dual-ended manipulation reduces the amount of room available to work on an item. In earlier machining equipment, one operated on the work piece from only one end of the equipment's turret or spindle. Present equipment, and CNC lathes in particular, permit the operator to work the piece from both sides of the turret. The ability to work on a piece from both sides of the equipment has greatly improved production capability. However, it has also reduced the space available to work on that piece. This is because the bed length of the machining equipment has remained essentially the same while the turret or spindle operates over a wider area than in the past. The present tool/piece securing means have failed to keep up with the improved capability of dual-end machining because they are limited to the extent that they permit an operator to place the tool or work piece all the way into the turret or spindle holder. In addition, the use of two securing components increases the overall length of the prior gripping devices. This length increase reduces the working space available on the equipment.
Another problem with prior securing devices involves the shank--the closing element used to retain the collet. It is well known that machining equipment of the type noted is made with various turret hole sizes. Since it is much less expensive to have a variety of collet and shank assemblies rather than a variety of machines, it has been necessary to adapt such assemblies to the turret/spindle holes. Present shanks come in a range of sizes designed to fit into the range of turret holes. For a shank of a particular size, only collets in a certain range of sizes can be used with that particular shank. A problem arises when the machine operator has a machine with a turret hole that requires a shank of a certain size, and a tool that requires a collet falling outside of the range of collets available for that certain shank. Generally, this occurs when the turret hole is large and the tool is small. In that situation, an adapter must be inserted into the turret hole in order to accommodate a smaller shank that will be able to retain a smaller collet. Unfortunately, the need to have this supplemental adapter increases the accumulation of error in matching the work tool to the work piece.
A further problem with the various shanks of the prior assemblies is the fact that different shanks have different securing components--larger shanks having larger securing components. Of course, with the larger shanks and securing components--particularly the generally-available securing components that are located on the exterior of the shank--comes a reduction in available working space.
Still another problem associated with present chucking devices is the expense involved. Collet assemblies currently available are most commonly made of hardened steel. Give the fact that tools and work pieces gripped in the collet vary greatly in size, it is necessary to stock a number of collets, even to the point that it is sometimes necessary to purchase a collet or collets for one-time use only. The cost to secure the tool or work piece is therefore considerable. In addition to the upfront expense of the present collets, the fact that they are made of hardened steel eliminates the possibility of easily modifying them to accommodate other work pieces or tools, by, for example, enlarging the bore hole into which the piece or tool is placed.
Therefore, what is needed is an assembly for securing tools and work pieces that can be locked and released from one end only, in order to provide the maximum possible space in which to work on the secured piece. What is also needed is an assembly for securing tools and work pieces that eliminates the need for a supplemental adapter used to accommodate the range of turret holes, spindle holes, work tools, and work pieces. Further, what is needed is a chucking device that can be made inexpensively and of materials machinable enough to be easily modified while still hard enough to provide sufficient strength to grip the tool or work piece therein under anticipated operating conditions.